1. Field of the Invention
The present invention relates to a complex sintering furnace that sequentially performs a bake-out process and a sintering process for molding ceramic products, and more particularly, to an ascending/descending apparatus and a complex sintering furnace using the same, which can obtain smooth gas flow and uniform temperature distribution. In the complex sintering furnace, the vertical transfer and rotation of a rotating base on which a plurality of ceramic moldings are loaded are simultaneously achieved so that a bake-out process and a sintering process can be simultaneously performed through the cylindrical furnace bodies arranged adjacent to each other.
2. Description of the Related Art
Examples of ceramic electronic products include multi-layer ceramic capacitor, ferrite, and piezoelectric devices. In a process of manufacturing the ceramic electronic products, ceramic materials are molded in a predetermined shape and a multi-layer ceramic molding is manufactured through a de-binder process, a sintering process, and a cooling process.
In the process of manufacturing the ceramic molding, slurry is formed by adding a binder (organic component) to raw material powder, such as BaTiO3, CaCa3, MnO, and Glass Frit. A ceramic sheet using the slurry as a dielectric sheet is molded. An internal electrode is pattern-printed on the surface of the ceramic sheet. The internal electrode is formed of a metal, such as Ni, Cu, Pd, and Pd/Ag. Such a ceramic sheet is stacked in multi-layers, thereby forming a multi-layer sheet. The multi-layer sheet is pressed under a pressure of 500-1300 kgf/cm2. Then, the pressed multi-layer sheet is cut into predetermined lengths, finally manufacturing the rectangular-parallelopiped ceramic molding.
A de-binder process, a sintering process, and a cooling process are sequentially performed on the ceramic molding. The de-binder process is to remove a binder component by baking out the ceramic molding at a temperature of 230-350° C. in the sintering furnace. The sintering process is to sinter the ceramic molding at a temperature of 900-1300° C. for 10-24 hours. The cooling process is to cool the ceramic molding at a low temperature after the sintering process. An external electrode and a terminal electrode are deposited on a periphery of the ceramic molding sintered in the sintering furnace. In this way, the ceramic product is completely manufactured.
A basic structure of a conventional complex sintering furnace will be described below with reference to FIGS. 1 and 2.
FIG. 1 is a perspective view of a conventional complex sintering furnace, and FIG. 2 is a perspective view of the conventional complex sintering furnace when a door is opened.
Referring to FIGS. 1 and 2, each of sintering furnaces 100, 200 and 300 includes a box-shaped furnace body 120 having a door 110 openably connected to the front surface. The furnace body 120 is divided into three sections, each of which has a receiving space 121 where a plurality of ceramic moldings C are received.
The furnace body 120 includes an inlet 122 on one side and an outlet 123 on the other side or same surface. Outside air is introduced through the inlet 122. A punched plate 124 with a plurality of holes is provided on both sidewalls of the furnace body 120.
In addition, the furnace body 120 includes a fan 125 on the top thereof. The fan 125 supplies outside air introduced through the inlet 122 into the inside of the receiving space 121. A heater 126 is mounted on one side of the fan 125 so as to heat the introduced outside air.
The conventional sintering furnaces 100, 200 and 300 uses a direct hot air circulation scheme in which the air introduced into the furnace body 120 through the inlet 122 is heated by the heater 126 and is supplied to the inside of the receiving space through the punched plate 124 disposed at each side of the furnace body 120.
That is, the hot air introduced into the furnace body 120 through the heater 126 and the punched plate 124 disposed at one side bakes out or sinters the ceramic moldings C stacked within the receiving spaces 121, and is discharged through the punched plate 124 disposed at the other side after the organic binder is removed from the ceramic molding C and the sintering process is completed.
However, in the conventional sintering furnaces 100, 200 and 300, the heating source is supplied to the ceramic moldings C through the fan 125 disposed on the top of the furnace body 120 in accordance with a hot air convection scheme. Therefore, hot air with a proper temperature is supplied to locations near the punched plate 124 that is the source of the hot air. Meanwhile, hot air with a relatively low temperature is inevitably supplied to locations far away from the punched plate 124. Consequently, a large temperature difference occurs in the furnace body 120.
In addition, a plurality of bake-out furnaces and a plurality of sintering furnaces are individually arranged at intervals of 20-30 m, as shown in FIG. 1. The bake-out process and the sintering process must be performed in the respective furnace bodies 120. Therefore, when the bake-out process for molding the ceramic product is completed in the first and second bake-out furnaces 100 and 200, an operator must manually transfer the ceramic molding C stacked inside the furnace body 120 of the furnace 100 to the next bake-out furnace 200. In addition, the operator must manually transfer the ceramic molding C to the furnace body 120 of the third sintering furnace 300 in order for sintering the ceramic molding C.
In such a conventional sintering furnace, it takes a lot of time to transfer the ceramic molding C so as to perform the bake-out process and the sintering process, and the operator must manually perform these processes. Consequently, the productivity is significantly degraded because the manufacturing time of the ceramic product is delayed as much. In addition, the cost of the product increases due to the increased personnel expenses.
Furthermore, as the molding process is performed, the ceramic products molded through the conventional sintering furnace 100 should be repetitively stacked and withdrawn through the bake-out furnaces and the sintering furnaces. Consequently, the product is not molded with uniform quality. In the structure of the furnace body for performing each process, cracks may occur due to the mismatch between ceramic component and metal component of the ceramic molding due to the difference between the bake-out temperature and the sintering temperature in the ceramic molding.